1. Field of the Invention
The invention relates generally to the assembly of integrated circuit boards, and particularly to improved methods for picking and placing oddly shaped components using a pick and place machine.
2. Background
In high volume circuit board assembly, a pick and place machine is typically used to pick up and place components onto circuit boards. The components are placed onto solder pads that are covered with solder paste. After the components are placed, the circuit board is heated, which melts the solder and attaches the component to the board. The components typically come in reels. Components that are too large or that are oddly shaped, and therefore cannot be taped and reeled, are typically placed in trays.
In order for the pick and place machine to pick up the components, there must be some way for the machine to “see” them. Without going into detail, a conventional pick and place machine usually includes a camera that allows it to see the parts after pick them up. The location of the corresponding solder pads can then be programmed into the machine so that it will “know” where to place a component once it has picked it up.
The process just described is generally used whether the components are in trays or on reels. The camera must be able to see all or substantially all of the component in order to allow the machine to place it on the solder pads. If a component is so large that it extends beyond the field of view of the camera used to see the component, then the process does not work very well. This is because, the pick and place machine is typically configured to locate a component by locating the center of the component. The center is usually determined with reference to the edge or outside dimensions of the component. Thus, if a component does not fit within the field of view of the camera, then the camera will not be able to locate the center, because it will not be able to reference the edges of the component, and the pick and place machine will not be able to pick up the component.
This problem is prevalent, for example, in the assembly of circuit boards for mobile phones. In particular, many mobile phones include a Radio Frequency (RF) test port that “picks-off” RF signal generated by the mobile phone just before they reach the antenna. This, for example, allows a technician to test the performance of the phone. A low loss transmission line is needed to connect the test port to the pick-off point, which is near the antenna. A piece of coaxial cable is typically used as the transmission line. The cable can be several centimeters to several inches. Thus, the cable often extends well beyond the field of view of the camera, which means the center of the cable cannot be locate efficiently.
As a result, it is difficult to use conventional pick and place machines to place such cables. It should be clear, however, that the same or similar problem attaches whenever a component is of such dimension that it makes it difficult for the pick and place machine to locate the center of the component.
The conventional solution to this problem is to hand place the components onto the circuit board. The hand placed components can then be solder onto the board by hand after all the other parts have been attached via the heating process described above, or the component can be hand placed and then attached via the heating process along with the rest of the components.
Hand placing such components, however, has severe drawbacks, namely an increase in the cost of production, because hand placing components is time consuming. Conventional pick and place machines can place thousands of parts very quickly and very accurately. Whereas hand placing parts is a much slower and more methodical process. But in high volume production, even minor slow downs can be very costly in monetary terms. Further, it takes extra personal to hand place the parts, which also drives up costs significantly.
Alternatively, The cable can be manufactured with connectors on each end. Mating connectors can then be placed and soldered onto the board using a conventional pick and place machine. The cable can then be attached by hand using the connectors. While this may save some assembly time, it still drives up labor costs and increases the cost of the cable and the circuit board due to the added connectors.
The bottom line is that it is not only inefficient to have to hand place components in a high volume assembly process—it is also very costly.